Starch consists of a mixture of amylose (15-30% w/w) and amylopectin (70-85% w/w). Amylose consists of linear chains of α-1,4-linked glucose units having a molecular weight (MW) from about 60,000 to about 800,000. Amylopectin is a branched polymer containing α-1,6 branch points every 24-30 glucose units; its MW may be as high as 100 million.
Sugars from starch, in the form of concentrated dextrose syrups, are currently produced by an enzyme catalyzed process involving: (1) liquefaction (or viscosity reduction) of solid starch with an α-amylase into dextrins having an average degree of polymerization of about 7-10, and (2) saccharification of the resulting liquefied starch (i.e. starch hydrolysate) with amyloglucosidase (also called glucoamylase or GA). The resulting syrup has a high glucose content. Much of the glucose syrup that is commercially produced is subsequently enzymatically isomerized to a dextrose/fructose mixture known as isosyrup. The resulting syrup also may be fermented with microorganisms, such as yeast, to produce commercial products including ethanol, citric acid, lactic acid, succinic acid, itaconic acid, monosodium glutamate, gluconates, lysine, other organic acids, other amino acids, and other biochemicals, for example. Fermentation and saccharification can be conducted simultaneously (i.e., an SSF process) to achieve greater economy and efficiency.
α-Amylases hydrolyze starch, glycogen, and related polysaccharides by cleaving internal α-1,4-glucosidic bonds at random. α-Amylases, particularly from Bacilli, have been used for a variety of different purposes, including starch liquefaction and saccharification, textile desizing, starch modification in the paper and pulp industry, brewing, baking, production of syrups for the food industry, production of feedstocks for fermentation processes, and in animal feed to increase digestability. These enzymes can also be used to remove starchy soils and stains during dishwashing and laundry washing.
Several Aspergillus species, including A. fumigatus, show intermediate or weak amylolytic behavior. See Nehira et al. (1956) “Taxonomic studies on the genus Aspergillus. VIII. The relation between the morphological characteristics and the amylolytic properties in the Aspergillus,” Hakko Kogaku Zasshi 34: 391-99, 423-28, 457-63. A. fumigatus Fresenius, for example, is capable of secreting both an alpha-amylase and a glucoamylase. See Domingues et al. (1993) “Production of amylase by soil fungi and partial biochemical characterization of amylase of a selected strain (Aspergillus fumigatus Fresenius),” Can. J. Microbiol. 39: 681-685; see also Goto et al. (1998) “Production of amylase by Aspergillus fumigatus utilizing α-methyl-D-glycoside, a synthetic analogue of maltose, as substrate,” FEMS Microbiol. Lett. 167: 139-143. The optimal pH and temperature were found to be 6.0 and 50° C., respectively, for both the alpha-amylase and glucoamylase from A. fumigatus Fresenius. Domingues et al. (1993) Can. J. Microbiol. 39: 681-685.